Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.97   10.626%   $219.0063   $219.01   $219.00   $219.00  
  Purchase #2 $40.25   9.817%   $44.2013   $44.20   $44.20   $44.20  
  Purchase #3 $94.75   5.108%   $99.5898   $99.59   $99.60   $99.60  
  Purchase #4 $26.67   7.811%   $28.7532   $28.75   $28.75   $28.80  
  Purchase #5 $87.80   6.476%   $93.4859   $93.49   $93.50   $93.50  
  Purchase #6 $177.66   12.254%   $199.4305   $199.43   $199.45   $199.40  
  Purchase #7 $58.79   10.842%   $65.164   $65.16   $65.15   $65.20  
  7 purchase totals = $683.89       $749.6310   $749.63   $749.65   $749.70